The present embodiments relate to color Doppler, color flow, or other motion imaging using ultrasound. In particular, higher frame rate motion imaging is provided with reduced line artifacts.
Parallel receive beamformation may incease ultrasound imaging frame rate. However, parallel receive beamformation may introduce line artifacts in color Doppler images due to the misalignment between the transmit (tx) and receive (rx) beams. In color Doppler imaging, velocity is often calculated based on the assumption that the normal direction of the echo wavefront is aligned with the receive beam. This assumption is not always met when there is a misalignment between transmit and receive beams. The angular deviation of the normal direction of the echo wavefront from the receive beam produces biases in the velocity estimates. The receive beams on opposite sides of a transmit beam cause biases with different signs, which reveals as beam group artifacts in the image.
Spatial filtering is typically used to overcome the line artifact, but spatial filtering may degrade the resolution. When the number of parallel receive beams per transmit beam increases for more rapid scanning, the line artifact becomes more severe, and eventually may not be managed with spatial filters. Though advanced modern ultrasound systems are capable of processing a large number of parallel receive beams, line artifact limits the number of parallel receive beams in color Doppler imaging (e.g., limited to four parallel receive beams). To increase the frame rate, color images either lack details due to spatial smoothing or show too much line artifact.
In one approach to address this dilemma, estimates from overlapping beams acquired from two adjacent transmit groups are linearly interpolated. The linear interpolation of the velocity estimates may be effective when all the receive beams are well covered by the transmit beams. Complete overlap in the receive beams between adjacent transmit beam groups is used, but complete overlaps may limit the frame rate. The linear interpolation is limited to pairs of collinear receive beams. Other approaches may compound for more than two collocated receive beams and loosen the need for complete overlap of the receive beams from adjacent beam groups, but rely on combining velocity estimates with opposite signs of the bias, creating a spatial distribution requirement for the scanning.